Defense lawyers bid to damage Gates’s credibility by asking if he failed to disclose four affairs – prompting an instant objection

Rick Gates on the witness stand in court in Alexandria. Gates is testifying against Paul Manafort, an ex-Trump campaign chairman accused of bank fraud and tax evasion.Photograph: Dana Verkouteren/AP

Defence lawyers for Paul Manafort made a last-ditch attempt on Wednesday to torpedo the key witness at his trial by asking whether he failed to disclose four extramarital affairs.

Attorney Kevin Downing suggested the revelation would destroy Rick Gates’s plea agreement with the special counsel’s office but was blocked by an instant government objection.

The drama came at the end of Gates’s testimony in the trial of his former boss and mentor Manafort, an ex-Donald Trump campaign chairman accused of bank fraud and tax evasion.

Manafort and Gates were the first two individuals indicted in Mueller’s investigation into potential collusion between Russia and the Trump campaign. The case has little to do with either man’s work for the Trump campaign, which has only tangentially figured in the trial.

In a final back and forth between lawyers over Gates’s credibility, the focus turned to his decision to plead guilty and cooperate with special counsel Robert Mueller’s investigation, which Manafort’s defence have portrayed as an attempt to save his own skin.

Gates told the court in Alexandria, Virginia, that he had met with government lawyer Greg Andres and FBI agents 20 times and been told only to tell the truth, without any guarantee that he will be spared prison. Andres put it to him: “As you sit here today, do you have any doubt that if you lie, the special counsel’s office will rip up your plea agreement?”

Gates said he did not.

Downing then noted how on Tuesday he had referred to the witness’s “secret life”, in particular an extra-marital affair he conducted in London, that involved lavish spending on flights and hotels. “You said you had a made mistake,” the lawyer said.

Gates agreed.

Downing followed up: “Do you remember telling the office of the special counsel you actually engaged in four extramarital affairs?”

Andres quickly rose to his feet to interrupt: “Objection! Relevance.”

Downing responded that the question goes to whether Gates told the truth to the special counsel or whether the plea agreement should be ripped up – potentially devastating to the government’s case and to the public perception of special counsel Robert Mueller’s investigation into Russian election interference.

Judge TS Ellis III called both legal teams to the bench for a private conference. A device was activated to generate white noise so their conversation could not be heard. People in the packed public gallery could only try to lip read as they saw a grim-faced Andres make a series of hand gestures.

Gates, meanwhile, wearing dark blue suit, white shirt and red tie, cut a lonely figure at the witness stand, blinking hard. His seat was turned at such an angle that there was no risk of eye contact with Manafort.

After about five minutes, the judge and lawyers returned to their positions, and Downing appeared to have lost the battle. He asked a broader question about Gates spending beyond his means to fund a secret life.

“Mr Downing, I’ve made many mistakes over many years,” said Gates, before being cut off by the judge, who snapped: “This isn’t the time for that.”

Gates’s testimony wrapped moment later.

Gates, also a former Trump campaign aide, has claimed during three days of evidence that he both stole for and stole from Manafort, who denies 18 counts of bank and tax fraud and failing to disclose foreign bank accounts. He testified that he and Manafort knew they were committing crimes for years, concealing money in foreign bank accounts and falsifying bank loan documents.

On Wednesday, Gates initially testified Manafort told him to be truthful during a 2014 interview with the FBI about offshore shell companies and bank accounts that contained millions of dollars in proceeds from their Ukrainian political work. However, Gates also said the agents did not ask about tax returns and “the majority of the Cypriot accounts were closed” at the stage.

Andres questioned: “Did you tell the FBI there was hidden income in those accounts?”

“No,” Gates said.

The interview was part of an FBI investigation that sought to recover assets looted from the Ukrainian government under former president Viktor Yanukovych. Gates and Manafort were not targets of the FBI at the time of the interview.

More recently, after the launch of the Mueller investigation but before his plea bargain, Gates lied to the FBI about a meeting between Manafort and an unnamed US Congressman regarding a “specific issue”. The meeting has previously been cited in court documents.

“You knowingly made a false statement to the FBI?” Andres asked on Wednesday. “Yes,” Gates answered.